The present invention is directed to an underdrain distributor assembly for use in a liquid filter of the type having a granular filter bed through which the liquid to be treated flows downwardly therethrough.
Granular media filters, as used extensively for the purification of water, typically comprise a carefully graded particulate media filter bed of sand, anthracite, etc., which filter bed is supported above a floor positioned in a filter tank so as to divide the tank into an inlet chamber thereabove and an outlet chamber therebelow. In use, as the water to be treated is passed downwardly through the filter bed, the suspended solids are removed and retained within the granular media. Periodically, it is necessary to remove the suspended solids collected in the filter bed by backwashing the filter bed so as to preclude the filter from clogging and ceasing to properly function. Backwashing is conventionally achieved by passing backwash water upwardly through the filter media, preferably preceeded by or accompanied by a backwash gas such as air.
The collection of filtrate and the distribution of backwash air and/or water is commonly achieved by specially designed strainers or underdrain distributors which are received through openings in the floor of the filter tank and connect with pipes or a plenum space beneath the floor. It is particularly advantageous that the underdrain distributors fit closely to the floor and that they uniformly distribute the backwash air and/or water over the entire area of the filter bed. Examples of such stainers and underdrain distributors are discussed in U.S. Pat. Nos. 3,730,348 and 4,214,992.
While the heretofore proposed strainers and underdrain distributors have been effective in directing backwash air and/or water upwardly through the filter bed, they have resulted in what, in essence, is a point source of the backwash air and/or water. In so doing, the backwash air and/or water is not uniformly distributed over the entire area of the filter bed and thereby creates dead spots therein.